1. Field of the Invention
The present arrangement concerns a packing arrangement for sealing, with a non-rotating annular packing, the surface of a rotary drum-like object, such as a washing drum used in cellulose manufacturing, said packing being most advantageously composed of one or several side-by-side packing fillets, e.g. braided packings, such arrangement comprising a circular packing body which, together with the rotating drum surface, defines a space in which the packings have been installed.
2. Description of Related Art
In present art, braided packings of this type are tightened to appropriate tightness with the aid of a spider ring attached with a screw to the packing body. When the screw is tightened, the box cords are increasingly compressed in the packing box and act on the surface of the rotating drum with greater force. When the tightness is appropriate, the packing operates fairly well as long as there are no configurational inaccuracies of the drum surface, e.g. owing to manufacturing defects or thermal expansion phenomena. If the rotation of the drum is even slightly eccentric, for istance owing to shaft off-set, friction forces of different magnitude act on the packing at different points and the packig suffers abnormal wear. Furthermore, this gives rise to an extra torque component. As a consequence of its wear, the packing begins to leak over the course of time. Such leakage can be temporarily stopped by tightening the packing, but this clearly also entails an even further increase of the friction forces and the packing suffers still worse wear, causing the leakage to eventually increase. Thus, the packing becomes unfit for use in a relatively short time, and it must be replaced. Apart from the wear experienced by the packing, the surface which the packing contacts is also abraded when the tightening is increased.
Traditionally, the thickness of the packing fillet is dimensioned in relation to the diameter of the sealing surface. In the packing instruction, the ratio between the thickness of the packing and the diameter of the sealing surface should be greater than 0.1. When this condition is met, the resilience of the packing material will eliminate the above-mentioned inaccuracies in manufacture as well as other deformations and thermal expansion effects. It is, however, not sensible in practice to construct packings thick enough for large diameters that have to be sealed off, because their manufacturing would be exceedingly expensive.